Operational fluid for a vapour circuit processing device and a method for operating same

ABSTRACT

The invention relates to an operating fluid for a steam cycle process apparatus comprising a steam generator, an expander, a condenser and a reservoir for the operating fluid, comprising a working medium that evaporates by supplying heat in the steam generator, performs mechanical work in the vapour phase by expanding in the expander and condenses in the condenser and an ionic liquid which forms a mixture with the working medium, wherein the melting point of the mixture lies below −5° C.

The invention relates to an operating fluid for a steam cycle process apparatus, a method for the operation thereof and a suitable steam cycle process apparatus for implementing the method.

Steam cycle processes are used to convert thermal energy into mechanical energy and are used, for example, for power generating units which generate a heat flow by means of a burner device, which is fed to a steam generator. In the steam generator, a working medium is evaporated by supplying heat, wherein the vapour phase thus produced expands whilst performing mechanical work in an expander and then condenses in a condenser. Typically, the condensate is supplied to a reservoir from which a renewed inflow to the steam generator is accomplished by means of a feed pump for the working medium.

A steam engine can furthermore be used to utilise the waste heat of an internal combustion engine, whereby, for example, its exhaust gas flow is fed to a heat exchanger device in the steam generator. Alternatively or additionally, it is possible to use the waste heat in the cooling water of an internal combustion engine to operate a steam cycle process. The mechanical work produced in the expander can then be supplied at least indirectly to a shaft of the drive system or an electrical generator is driven by the expander. In this way, an apparatus for executing a steam cycle process can be configured as an auxiliary unit utilising the waste heat of a main engine which either provides motor assistance to the propulsion of the vehicle or provides electrical energy for secondary consumers.

In order to achieve a high efficiency, the requirement is fundamentally imposed on the working medium for operating the steam cycle process that there is a large temperature difference between the vapour phase and the condensate. This requires that the working medium remains thermally stable up to high temperatures, typically above 400° C. Furthermore, there are further requirements with regard to the corrosion protection of the steam generation apparatus and transport of lubricants in the vapour phase, in particular for executing a self-lubrication of the moving components of the expander. In addition, revolving components of the drive system need to be lubricated, wherein a separate lubricant circuit with a separate lubricant from the working medium for operating the steam engine is typically provided for this purpose. Furthermore, during a non-continuous operation, in particular for use in a vehicle, an extended standstill of the steam cycle process at simultaneously low ambient temperatures should be taken into account, so that measures for frost protection must be taken.

Accordingly the operating fluid for a steam cycle process comprises additives to the working medium. These can form an azeotrope with the working medium. An example for this is disclosed by DE 103 28 289 B3, which proposes as operating fluid for a steam cycle process, a mixture of water and at least one heterocyclic compound as well as additional, miscible polymers, tenside and/or other organic lubricants. In particular, 2-methyl pyridine, 3-methyl pyridine, pyridine, pyrrole and pyridazine are suggested as heterocyclic compound. As a result of the use of the hetercyclic compound, the freezing point of the operating fluid is set below 0° C. At the same time, the heterocyclic compound forms an azeotrope with water so that this goes over into the gas phase together with the water fraction in the steam generator. In so doing, lubricant is also transported to the expander in the vapour phase for executing a self-lubrication.

A disadvantage of the known operating fluids for steam cycle processes is their toxicity so that expensive precautions must be taken to reliably prevent any escape of the operating fluid or its gas phase. When used in vehicles, in particular in motor vehicles, this cannot however be completely eliminated in view of possible accident risks.

It is therefore the object of the invention to provide an operating fluid for a steam cycle process which, in particular for discontinuous operation and for extended standstill times, enables a cold start of the steam cycle process at any time, even at low ambient temperature, and in particular ensures the frost protection safety of the system. At the same time, the operating fluid should be environmentally compatible and in particular not toxic for plants and living organisms and should be characterised by a high accident safety. In addition, a further object of the invention is to provide a method by which means the steam cycle process can be operated with the operating fluid such that this is configured as energy-efficiently as possible, as well as an apparatus for executing the method. For a further embodiment of the invention, the operating fluid for the steam cycle process should additionally be used for the lubrication of the revolving components of the steam engine and in the case of a vehicle application, preferably for the lubrication of the moving parts of the drive system including the internal combustion engine.

The object of the invention is achieved by the operating fluid comprising at least two components. The first component is a working medium which is used for the actual operation of the steam cycle process. Accordingly, evaporation of the working medium is accomplished by supplying heat in the steam generator, a subsequent expansion takes place in the expander whilst performing mechanical work and then condensation takes place whilst returning the condensate, typically via a reservoir and a feed pump, for renewed entry into the cycle, that is, for renewed evaporation in the steam generator.

A further component of the operating fluid for the steam cycle process according to the invention is a frost protection agent that under normal operating conditions undergoes substantially no evaporation in the steam generator and merely serves to keep the operating liquid in the reservoir liquid at low external temperature and therefore to allow a cold starting of the system. Advantageously the frost protection agent simultaneously exhibits lubricant properties.

According to the invention, an ionic liquid is used as frost protection agent, wherein the mixture of ionic liquid and working medium has a melting point which lies below the freezing point of the pure working medium. In the present case, water is used as the preferred working medium so that a melting point for the mixture of the selected ionic liquid and water lies below 0° C. A melting point below −5° C. is preferred, particularly preferably below −10° C. and especially preferably below −30° C. In the present case, a pressure of 1 bar is assumed for all the temperature information. A mixture between an ionic liquid suitable for frost protection and the working medium is understood in the present case such that each of the two components is present in the mixture at least with a minimum weight fraction of 0.01 gw. % (percent by weight). Preferably no complex formations should be present in the mixture between the ionic liquid and the working medium so that no substantial binding forces need to be broken to evaporate the working medium.

A mixture of ionic liquid and working medium according to the invention having a fraction of 99.99 gw. % (percent by weight) to 0.01 gw. % (percent by weight) working medium accordingly has a melting point for the mixture that lies below 0° C., preferably below −5° C. and particularly preferably below −10° C. and further preferably below −30° C. At the same time, it is possible that the ionic liquid used for the mixture in pure form has a melting point which lies above the freezing point of the pure working medium. For example, an ionic liquid can be used which in pure form melts in the temperature range of 0-100° C. The required frost protection effect accordingly consists in the mixture of ionic liquid and working medium. In this context, the melting point of the mixture in the present case is understood as the temperature of the crystallisation boundary of the mixture so that the mixture is liquid above the melting point and can be pumped from the reservoir.

In general, the melting point of the mixture is dependent on the mixing ratio between ionic liquid and working medium. In this context, for an operating fluid according to the invention, the feature of a melting point lying below the freezing point of the pure working medium should apply at least in a mixing ratio range which is present in a collecting reservoir of a cold, stopped steam cycle process apparatus. Preferably a weight fraction of the working medium of at least 10 gw. % and at most 90 gw. % is assumed, the range of 20 gw. % (percent by weight) to 80 gw. % (percent by weight) being more strongly preferred for the fraction of working medium. For the case of a cold system it is particularly preferred that the weight ratio of the ionic liquid to working medium lies in the range of 60:40 to 40:60.

Furthermore, the case can arise that the previously specified reference pressure of 1 bar is exceeded or fallen below in certain operating phases or parts of the steam cycle process apparatus. Insofar as a deviation from the reference pressure of 1 bar exists at a standstill for a cold frost-endangered reservoir, the previously specified temperature condition relating to the melting point of the mixture of ionic liquid and working medium should be valid for the prevailing system pressure. Hereinafter for simplicity a ventilated reservoir for the operating fluid is assumed.

During operation, the mixing ratio in the operating fluid can shift with increasing temperature. This can lead to substantially complete separation of the ionic liquid from the working medium. At the same time, it is feasible within the framework of the invention that during operation at temperature the mixing ratio shifts so far that the temperature condition for the melting point of the mixture as lying below the freezing point of the working medium is no longer satisfied for certain operating phases. This will still be understood as part of the invention. After the installation has come to a standstill, the mixing ratio is restored again in a collecting reservoir in order to ensure the frost safety again.

Ionic liquids owe their low melting point to a poor ionic coordination. The delocalised charges are responsible for this, wherein typically at least one ion is based on an organic molecule and the formation of a stable crystal lattice is already prevented at low temperatures.

Typical for ionic liquids is the possibility of selecting their physical/chemical properties through the choice of cation/anion pairing so that it is possible to tailor an ionic liquid for the operating fluid according to the invention for the steam cycle process such that when mixed with the working medium, a low melting point is formed in the sense of a frost protection effect.

A particular advantage of ionic liquids for use as part of an operating fluid for a steam cycle process can be seen in that the ionic liquid is characterised by a vanishing vapour pressure up to its decomposition temperature. If the decomposition temperature is adjusted by means of a corresponding choice of the cation/anion pairing for the ionic liquid such that this lies above the temperature of the liquid phase of the operating fluid in the steam generator, it is possible that the ionic liquid does not go over into the gas phase and is passed to the expander like the actual working medium. As a result, a simple possibility for separating the ionic liquid from the operating fluid is obtained for the case that the operating temperature of the steam cycle process is reached or that a temperature is present in the system at which frost safety is no longer necessary.

After separating the ionic liquid from the operating fluid, for operation at temperature the energetically disadvantageous case can be prevented that the frost protection agent component, that is the ionic liquid, must be heated in the steam generator without making an energy contribution in the steam cycle. The extracted ionic liquid or a branched-off mixture enriched with ionic liquid containing a reduced fraction of working medium can be used for a further embodiment of the invention for lubrication. In the steam cycle process apparatus, in particular the expander lubrication, comes into consideration for this. In vehicle applications, further components to be lubricated can be supplied. This also includes the lubrication of revolving parts of an internal combustion engine which is combined with a steam engine as a hybrid drive.

According to an advantageous embodiment, the operating method comprises the following operations:

The starting point is initially the steam cycle process being at a standstill at cold external temperatures. In this case, the operating fluid is collected in a reservoir and contains a mixture comprising the working medium that is provided for evaporation in the steam generator and the ionic liquid which acts as a frost protection agent in the mixture, so that even at low external temperatures when the steam cycle process is at a standstill, the operating fluid is present in liquid form in a reservoir.

When starting the steam cycle process, thermal energy, for example, via an exhaust gas flow stream from an internal combustion engine, is supplied to the steam generator. At the same time, the operating fluid enters into the steam generator. The supply can be accomplished, for example, by means of a feed pump. In the steam generator, evaporation of the working medium takes place whilst the ionic liquid produces a vapour pressure which tends to zero and is returned to the reservoir. According to an alternative embodiment, said liquid is not returned to a reservoir but to a separate tank for an ionic liquid.

After it has expanded and performed work in the expander, the vaporous working medium is fed to the condenser, wherein according to an advantageous embodiment the condensate of the working medium thus formed is not returned to the reservoir but is fed to a separate tank for the working medium. A continuous separation of the ionic liquid and the working medium is produced by this measure. In this case, it should be noted that this separation should advantageously only be made above a specific operating temperature. The operating temperature can therefore be measured at various positions in the apparatus for executing the steam cycle process, wherein the operating fluid in the reservoir can advantageously be used at the location of the temperature measurement. If a specific temperature which lies above the freezing point of the working medium is reached in the reservoir, the previously described separation of the working medium and the ionic liquid can be made. Various separation methods can be used here.

After a certain time and/or on reaching a certain level in the tank for the working medium a switching can be undertaken and the reservoir separated from the steam generator and instead, an exclusive supply of liquid takes place from the tank for the working medium. This switching characterises the operation of the steam cycle process at temperature, in which substantially the working medium without the ionic liquid comes in contact with the heat flow in the steam generator and runs through the steam cycle process. For a further embodiment of the invention, it is possible to use the mixture enriched with ionic liquid in the reservoir for lubrication purposes.

When the steam cycle process is again at a standstill, at correspondingly low ambient temperature, the separated ionic liquid can be combined with the further components of the operating fluid. Advantageously, a mixing only takes place below a lower limiting temperature in the reservoir for the operating fluid. According to a simplified embodiment, the renewed mixing can also take place after a predetermined time interval after switching off the steam cycle process or one of its partial components, for example, the feed pump for the volume flow to the steam generator.

Alternatively, the separation of the ionic liquid and the working medium during operation of the steam cycle process can take place such that after running through the steam generator, the operating fluid is passed through a separator in which the vaporous working medium is separated. In the liquid phase the ionic liquid is enriched as a result of the partial pressure which tends to zero, and can be extracted into a separate reservoir. For a further development of the invention, a lubrication circuit can be supplied from this reservoir, wherein in addition to the frost protection effect, the lubrication properties of the ionic liquid or a mixture enriched with this can advantageously be utilised.

In addition, the possibility set out hereinbefore of using the ionic liquid as a frost protection agent or as a combined frost protection agent and lubricant that can be removed from the steam cycle during operation to temperature, ionic liquids are characterised by further advantageous properties. Ionic liquids are typically not combustible, they are electrically conductive and thus suppress the build-up of flow potentials. Furthermore, their viscosity and density and their mixing behaviour with other liquids can be adjusted in a wide range through the choice of the cation/anion pairing.

In particular, ionic liquids come into consideration which contain as anion a C1 to C4 alkyl sulphonate, preferably methyl sulphonate or a completely or partially fluorinated C1 to C4 alkyl sulphonate, preferably trifluoromethyl sulphonate.

Particularly preferred ionic liquids are those containing a cation of the formula IV a (pyridinium) or IV e (imidazolium) or IV x (phosphonium) or IV y (morpholinium) and as anion a C1 to C4 alkyl sulphonate, preferably methyl sulphonate or a completely or partially fluorinated C1 to C4 alkyl sulphonate, preferably trifluoromethyl sulphonate, or in a quite particularly preferred embodiment consist exclusively of such a cation and anion.

In the present case, the following definition for ionic liquids is taken as the starting point for implementing the invention, wherein two or generally more ionic liquids according to the following listing can be present in the mixture with the working medium:

An ionic liquid is a salt having a melting point below 100° C. at 1 bar.

The ionic liquid preferably has a melting point below 70° C., particularly preferably below 30° C. and quite particularly preferably below 0° C. at 1 bar.

In a particularly preferred embodiment, the ionic liquid is liquid under normal conditions (1 bar, 21° C.), that is at room temperature.

Preferred ionic liquids contain at least one organic compound as a cation, quite particularly preferably they contain exclusively organic compounds as cations.

Suitable organic cations are in particular organic compounds with heteroatoms such as nitrogen, sulphur or phosphorus. Particularly preferably these comprise organic compounds with at least one, preferably precisely one cationic group selected from an ammonium group, an oxonium group, a sulphonium group or a phosphonium group.

In a particular embodiment, the ionic liquids comprise salts with ammonium cations which are understood to be compounds with quadricovalent nitrogen and positive charge localised at nitrogen or aromatic ring systems with at least one, preferably one or two, particularly preferably two nitrogen atoms in the ring system and a delocalised positive charge.

Particularly preferred ammonium cations are the imidazolium cations, which are understood to be all compounds having an imidazolium ring system and possibly arbitrary substituents at the carbon and/or nitrogen atoms of the ring system.

The anion can comprise an organic or inorganic anion. Particularly preferred ionic liquids consist exclusively of the salt of an organic cation with one of the anions named hereinafter.

The molar weight of the ionic liquids is preferably less than 2000 g/mol, particularly preferably less than 1500 g/mol, particularly preferably less than 1000 g/mol and quite particularly preferably less than 750 g/mol; in a particular embodiment the molar weight is between 100 and 750 or between 100 and 500 g/mol.

Suitable ionic liquids are in particular salts having the following general formula I

[A]_(n) ⁺[Y]^(n−)  (I)

where n denotes 1, 2, 3 or 4, [A]⁺ denotes an ammonium cation, an oxonium cation, a sulphonium cation or a phosphonium cation and [Y]^(n−) denotes a mono-, di-, tri- or tetravalent anion;

or mixtures of salts having the general formula (II)

[A¹]⁺[A²]⁺[Y]²⁻  (IIa);

[A¹]⁺[A²]⁺[A³]⁺[Y]³⁻  (IIb); or

[A¹]⁺[A²]⁺[A³]⁺[A⁴]⁺[Y]⁴⁻  (IIc),

wherein [A¹]⁺, [A²]⁺, [A³]⁺ and [A⁴]⁺ are selected independently of one another from the groups specified for [A]⁺ and [Y]^(n−) have the meaning specified under B1); or

or mixed salts having the general formulae (III)

[A¹]⁺[A²]⁺[A³]⁺[M¹]⁺[Y]⁴⁻  (IIIa);

[A¹]⁺[A²]⁺[M¹]⁺[M²]⁺[Y]⁴⁻  (IIIb);

[A¹]⁺[M¹]⁺[M²]⁺[M³]⁺[Y]⁴⁻  (IIIc);

[A¹]⁺[A²]⁺[M¹]⁺[Y]³⁻  (IIId);

[A¹]⁺[M¹]⁺[M²]⁺[Y]³⁻  (IIIe);

[A¹]⁺[M¹]⁺[Y]²⁻  (IIIf);

[A¹]⁺[A²]⁺[M⁴]²⁺[Y]⁴⁻  (IIIg);

[A¹]⁺[M¹]⁺[M⁴]²⁺[Y]⁴⁻  (IIIh);

[A¹]⁺[M⁵]³⁺[Y]⁴⁻  (IIIi); or

[A¹]⁺[M⁴]²⁺[Y]³⁻  (IIIj)

wherein [A¹]⁺, [A²]⁺ and [A³]⁺ are selected independently of one another from the groups specified for [A]⁺, [Y]^(n−) has the meaning specified under B1) and [M¹]⁺, [M²]⁺, [M³]⁺ denote monovalent metal cations, [M⁴]²⁺ denote divalent metal cations and [M⁵]³⁺ denote trivalent metal cations;

or mixtures thereof.

Preferred are ionic liquids in which the cation [A]⁺ is an ammonium cation which generally contains 1 to 5, preferably 1 to 3 and particularly preferably 1 to 2 nitrogen atoms.

Suitable cations are, for example, the cations of the general formulae (IVa) to (IVy)

as well as oligomers containing these structures.

Morpholinium can furthermore be selected.

Another suitable cation is a phosphonium cation having the general formula (IVy)

as well as oligomers containing this structure.

In the aforementioned formulae (IVa) to (IVy)

the group R denotes a carbon-containing organic, saturated or unsaturated, acyclic or cyclic, aliphatic, aromatic or araliphatic, unsubstituted or interrupted by 1 to 5 heteroatoms or functional groups, or substituted group having 1 to 20 carbon atoms; and

the groups R¹ to R⁹ independently of one another can denote hydrogen, a sulpho-group or a carbon-containing organic, saturated or unsaturated, acyclic or cyclic, aliphatic, aromatic or araliphatic, unsubstituted or interrupted by 1 to 5 heteroatoms or functional groups, or substituted group having 1 to 20 carbon atoms, wherein the groups R1 to R9, which in the aforesaid formulae (IV) are bound to a carbon atom (and not to a heteroatom), can additionally also denote halogen or a functional group; or

two neighbouring groups from the series R¹ to R⁹ together can also denote a divalent carbon-containing organic, saturated or unsaturated, acyclic or cyclic, aliphatic, aromatic or araliphatic, unsubstituted or interrupted by 1 to 5 heteroatoms or functional groups, or substituted group having 1 to 30 carbon atoms.

Possible heteroatoms in the definition of the groups R and R¹ to R⁹ are in principle all heteroatoms which are capable of formally replacing a —CH₂—, a —CH═, a —C≡ or a ═C═. If the carbon-containing group contains heteroatoms, oxygen, nitrogen, sulphur, phosphorus and silicon are preferred. As preferred groups, mention is made in particular of —O—, —S—, —SO—, —SO₂—, —NR′—, —N═, —PR′—, —POR′— and —SiR′₂—, wherein the groups R¹ comprise the remaining part of the carbon-containing group. In cases where the groups R¹ to R⁹ are bound to a carbon atom (and not a heteroatom) in the aforesaid formulae (IV), these can also be directly bound via the heteroatom.

Possible functional groups are in principle all functional groups which can be bound to a carbon atom or a heteroatom. As suitable examples, mention may be made of —OH (hydroxy), ═O (in particular as a carbonyl group), —NH₂ (amino), ═NH (imino), —COOH (carboxy), —CONH₂ (carboxamide), —SO₃H (sulpho) and —CN (cyano). Functional groups and heteroatoms can also be directly adjacent so that combinations of several neighbouring atoms such as —O— (ether), —S— (thioether), —COO— (ester), —CONH— (secondary amide) or —CONR′— (tertiary amide), are also comprised, for example, di-(C₁-C₄-alkyl)-amino, C₁-C₄-alkyloxy-carbonyl or C₁-C₄-alkyloxy.

As halogens mention is made of fluorine, chlorine, bromine and iodine.

The group R preferably denotes

unbranched or branched, unsubstituted or singly to multiply substituted with hydroxy, halogen, phenyl, cyano, C1- to C6-alkoxycarbonyl and/or sulphonic acid C1- to C18-alkyl having a total of 1 to 20 carbon atoms such as, for example methyl, ethyl, 1-propyl, 2-propyl, 1-butyl, 2-butyl, 2-methyl-1-propyl (isobutyl), 2-methyl-2-propyl (tert.-butyl), 1-pentyl, 2-pentyl, 3-pentyl, 2methyl-1-butyl, 3-methyl-1-butyl, 2 methyl-2-butyl, 3-methyl-2-butyl, 2,2-dimethyl-1-propyl, 1-hexyl, 2-hexyl, 3-hexyl, 2 methyl-1-pentyl, 3-methyl-1-pentyl, 4-methyl-1-pentyl, 2-methyl-2-pentyl, 3-methyl-2-pentyl, 4-methyl-2-pentyl, 2 methyl-3-pentyl, 3-methyl-3-pentyl, 2,2-dimethyl-1-butyl, 2,3-dimethyl-1-butyl, 3,3-dimethyl-1-butyl, 2-ethyl-1-butyl, 2,3-dimethyl-2-butyl, 3,3 dimethyl-2-butyl, 1-heptyl, 1-octyl, 1-nonyl, 1-decyl, 1-undecyl, 1-dodecyl, 1 tetradecyl, 1-hexadecyl, 1-octadecyl, 2-hydroxyethyl, benzyl, 3-phenylpropyl, 2 cyanoethyl, 2 (methoxycarbonyl)-ethyl, 2-(ethoxycarbonyl)-ethyl, 2-(n-butoxy-carbonyl)-ethyl, trifluoromethyl, difluoromethyl, fluoromethyl, pentafluoroethyl, heptafluoropropyl, heptafluoroisopropyl, nonafluorobutyl, nonafluoroisobutyl, undecylfluoropentyl, undecylfluoroisopentyl, 6-hydroxyhexyl and propylsulphonic acid; glycols, butyleneglycols and their oligomers having 1 to 100 units and a hydrogen or a C1- to C8-alkyl as terminal group such as, for example R^(A)O—(CHR^(B)—CH₂—O)_(p)—CHR^(B)—CH₂— or R^(A)O—(CH₂CH₂CH₂CH₂O)_(p)—CH₂CH₂CH₂CH₂O— where R^(A) and R^(B) are preferably hydrogen, methyl or ethyl and p is preferably 0 to 3, in particular 3-oxabutyl, 3-oxapentyl, 3,6-dioxaheptyl, 3,6-dioxaoctyl, 3,6,9-trioxadecyl, 3,6,9-trioxa-undecyl, 3,6,9,12-tetraoxatridecyl and 3,6,9,12-tetraoxatetradecyl; vinyl; and N,N-Di-C₁-C₆-alkylamino, such as, for example, N,N-dimethylamino and N,N-diethylamino.

Particularly preferably the group R denotes unbranched and unsubstituted C₁-C₁₈-alkyl, such as, for example, methyl, ethyl, 1-propyl, 1-butyl, 1-pentyl, 1-hexyl, 1-heptyl, 1-octyl, 1-decyl, 1-dodecyl, 1-tetradecyl, 1-hexadecyl, 1-octadecyl, in particular methyl, ethyl, 1-butyl and 1-octyl as well as CH₃O—(CH₂CH₂O)_(p)—CH₂CH₂— and CH₃CH₂O—(CH₂CH₂O)_(p)—CH₂CH₂— where p is equal to 0 to 3.

The groups R¹ to R⁹ independently of one another preferably denote

hydrogen;

halogen;

a functional group;

C₁-C₁₈-alkyl optionally substituted by functional groups, aryl, alkyl, aryloxy, alkyloxy, halogen, heteroatoms and/or heterocyclic compounds and/or interrupted by one or more oxygen and/or sulphur atoms and/or one or more substituted or unsubstituted imino groups;

C₂-C₁₈-alkenyl optionally substituted by functional groups, aryl, alkyl, aryloxy, alkyloxy, halogen, heteroatoms and/or heterocyclic compounds and/or interrupted by one or more oxygen and/or sulphur atoms and/or one or more substituted or unsubstituted imino groups;

C₆-C₁₂-aryl optionally substituted by functional groups, aryl, alkyl, aryloxy, alkyloxy, halogen, heteroatoms and/or heterocyclic compounds;

C₅-C₁₂-cycloalkyl optionally substituted by functional groups, aryl, alkyl, aryloxy, alkyloxy, halogen, heteroatoms and/or heterocyclic compounds;

C₅-C₁₂-cycloalkenyl optionally substituted by functional groups, aryl, alkyl, aryloxy, alkyloxy, halogen, heteroatoms and/or heterocyclic compounds; or

a five- to six-membered heterocyclic compound comprising oxygen, nitrogen and/or sulphur atoms optionally substituted by functional groups, aryl, alkyl, aryloxy, alkyloxy, halogen, heteroatoms and/or heterocyclic compounds; or

two neighbouring groups together denote an unsaturated, saturated or aromatic ring optionally substituted by functional groups, aryl, alkyl, aryloxy, alkyloxy, halogen, heteroatoms and/or heterocyclic compounds and optionally interrupted by one or more oxygen and/or sulphur atoms and/or one or more substituted or unsubstituted imino groups;

C₁- to C₁₈-alkyl optionally substituted by functional groups, aryl, alkyl, aryloxy, alkyloxy, halogen, heteroatoms and/or heterocyclic compounds preferably comprises methyl, ethyl, 1-propyl, 2-propyl, 1-butyl, 2-butyl, 2-methyl-1-propyl (isobutyl), 2-methyl-2-propyl (tert.-butyl), 1-pentyl, 2-pentyl, 3-pentyl, 2-methyl-1-butyl, 3-methyl-1-butyl, 2-methyl-2-butyl, 3-methyl-2-butyl, 2,2-dimethyl-1-propyl, 1-hexyl, 2-hexyl, 3-hexyl, 2-methyl-1-pentyl, 3-methyl-1-pentyl, 4-methyl-1-pentyl, 2-methyl-2-pentyl, 3-methyl-2-pentyl, 4-methyl-2-pentyl, 2-methyl-3-pentyl, 3-methyl-3-pentyl, 2,2-dimethyl-1-butyl, 2,3-dimethyl-1-butyl, 3,3-dimethyl-1-butyl, 2-ethyl-1-butyl, 2,3-dimethyl-2-butyl, 3,3-dimethyl-2-butyl, heptyl, octyl, 2-ethylhexyl, 2,4,4-trimethylpentyl, 1,1,3,3-tetramethylbutyl, 1-nonyl, 1-decyl, 1-undecyl, 1-dodecyl, 1-tridecyl, 1-tetradecyl, 1-pentadecyl, 1-hexadecyl, 1-heptadecyl, 1-octadecyl, cyclopentylmethyl, 2-cyclopentylethyl, 3-cyclopentylpropyl, cyclohexylmethyl, 2-cyclohexylethyl, 3-cyclohexylpropyl, benzyl (phenylmethyl), diphenylmethyl (benzhydryl), triphenylmethyl, 1-phenylethyl, 2-phenylethyl, 3-phenylpropyl, α,α-dimethylbenzyl, p-tolylmethyl, 1-(p-butylphenyl)-ethyl, p-chlorobenzyl, 2,4-dichlorobenzyl, p-methoxybenzyl, m-ethoxybenzyl, 2-cyanoethyl, 2-cyanopropyl, 2-methoxycarbonylethyl, 2-ethoxycarbonylethyl, 2-butoxycarbonylpropyl, 1,2-di-(methoxycarbonyl)-ethyl, methoxy, ethoxy, formyl, 1,3-dioxolan-2-yl, 1,3-dioxan-2-yl, 2-methyl-1,3-dioxolan-2-yl, 4-methyl-1,3-dioxolan-2-yl, 2-hydroxyethyl, 2-hydroxypropyl, 3-hydroxypropyl, 4-hydroxybutyl, 6-hydroxyhexyl, 2-aminoethyl, 2-aminopropyl, 3-aminopropyl, 4-aminobutyl, 6-aminohexyl, 2-methylaminoethyl, 2-methylaminopropyl, 3-methylaminopropyl, 4-methylaminobutyl, 6-methylaminohexyl, 2-dimethylaminoethyl, 2-dimethylaminopropyl, 3-dimethylaminopropyl, 4-dimethylaminobutyl, 6-dimethylaminohexyl, 2-hydroxy-2,2-dimethylethyl, 2-phenoxyethyl, 2-phenoxypropyl, 3-phenoxypropyl, 4-phenoxybutyl, 6-phenoxyhexyl, 2-methoxyethyl, 2-methoxypropyl, 3-methoxypropyl, 4-methoxybutyl, 6-methoxyhexyl, 2-ethoxyethyl, 2-ethoxypropyl, 3-ethoxypropyl, 4-ethoxybutyl, 6-ethoxyhexyl, acetyl, C_(q)F_(2(q−a)+(1−b))H_(2a+b) where q is 1 to 30, 0≦a≦q and b=0 or 1 (for example, CF₃, C₂F₅, CH₂CH₂—C_((q−2))F_(2(q−2)+1), C₆F₁₃, C₈F₁₇, C₁₀F₂₁, C₁₂F₂₅), chloromethyl, 2-chloroethyl, trichloromethyl, 1,1-dimethyl-2-chloroethyl, methoxymethyl, 2-butoxyethyl, diethoxymethyl, diethoxyethyl, 2-isopropoxyethyl, 2-butoxypropyl, 2-octyloxyethyl, 2-methoxyisopropyl, 2-(methoxycarbonyl)-ethyl, 2-(ethoxycarbonyl)-ethyl, 2-(n-butoxycarbonyl)-ethyl, butylthiomethyl, 2-dodecylthioethyl, 2-phenylthioethyl, ethyl, 5-hydroxy-3-oxa-pentyl, 8-hydroxy-3,6-dioxa-octyl, 11-hydroxy-3,6,9-trioxa-undecyl, 7-hydroxy-4-oxa-heptyl, 11-hydroxy-4,8-dioxa-undecyl, 15-hydroxy-4,8,12-trioxa-pentadecyl, 9-hydroxy-5-oxa-nonyl, 14-hydroxy-5,10-dioxa-tetradecyl, 5-methoxy-3-oxa-pentyl, 8-methoxy-3,6-dioxa-octyl, 11-methoxy-3,6,9-trioxa-undecyl, 7-methoxy-4-oxa-heptyl, 11-methoxy-4,8-dioxa-undecyl, 15-methoxy-4,8,12-trioxa-pentadecyl, 9-methoxy-5-oxa-nonyl, 14-methoxy-5,10-dioxa-tetradecyl, 5-ethoxy-3-oxa-pentyl, 8-ethoxy-3,6-dioxa-octyl, 11-ethoxy-3,6,9-trioxa-undecyl, 7-ethoxy-4-oxa-heptyl, 11-ethoxy-4,8-dioxa-undecyl, 15-ethoxy-4,8,12-trioxa-pentadecyl, 9-ethoxy-5-oxa-nonyl or 14-ethoxy-5,10-oxa-tetradecyl.

C₂-C₁₈-alkenyl optionally substituted by functional groups, aryl, alkyl, aryloxy, alkyloxy, halogen, heteroatoms and/or heterocyclic compounds and/or interrupted by one or more oxygen and/or sulphur atoms and/or one or more substituted or unsubstituted imino groups preferably comprises vinyl, 2-propenyl, 3-butenyl, cis-2-butenyl, trans-2-butenyl or C_(q)F_(2(q−a)−(1−b))H_(2a−b) where q≦30, 0≦a≦q and b=0 or 1.

C₆-C₁₂-aryl optionally substituted by functional groups, aryl, alkyl, aryloxy, alkyloxy, halogen, heteroatoms and/or heterocyclic compounds preferably comprises phenyl, tolyl, xylyl, α-naphthyl, β-naphthyl, 4-diphenylyl, chlorophenyl, dichlorophenyl, trichlorophenyl, difluorophenyl, methylphenyl, dimethylphenyl, trimethylphenyl, ethylphenyl, diethylphenyl, iso-propylphenyl, tert.-butylphenyl, dodecylphenyl, methoxyphenyl, dimethoxyphenyl, ethoxyphenyl, hexyloxyphenyl, methylnaphthyl, isopropylnaphthyl, chloronaphthyl, ethoxynaphthyl, 2,6-dimethylphenyl, 2,4,6-trimethylphenyl, 2,6-dimethoxyphenyl, 2,6-dichlorphenyl, 4-bromphenyl, 2-nitrophenyl, 4-nitrophenyl, 2,4-dinitrophenyl, 2,6-dinitrophenyl, 4-dimethylaminophenyl, 4-acetylphenyl, methoxyethylphenyl, ethoxymethylphenyl, methylthiophenyl, isopropylthiophenyl or tert.-butylthiophenyl or C₆F_((5−a))H_(a) where 0≦a≦5.

C₅- to C₁₂-cycloalkyl optionally substituted by functional groups, aryl, alkyl, aryloxy, alkyloxy, halogen, heteroatoms and/or heterocyclic compounds preferably comprises cyclopentyl, cyclohexyl, cyclooctyl, cyclododecyl, methylcyclopentyl, dimethylcyclopentyl, methylcyclohexyl, dimethylcyclohexyl, diethylcyclohexyl, butylcyclohexyl, methoxycyclohexyl, dimethoxycyclohexyl, diethoxycyclohexyl, butylthiocyclohexyl, chlorocyclohexyl, dichlorocyclohexyl, dichlorocyclopentyl, C_(q)F_(2(q−a)−(1−b))H_(2a−b) where q≦30, 0≦a≦q and b=0 or 1 as well as a saturated or unsaturated bicyclic system such as, for example, norbornyl or norbornenyl.

C₅-C₁₂-cycloalkenyl optionally substituted by functional groups, aryl, alkyl, aryloxy, alkyloxy, halogen, heteroatoms and/or heterocyclic compounds preferably comprises 3-cyclopentenyl, 2-cyclohexenyl, 3-cyclohexenyl, 2,5-cyclohexadienyl or C_(q)F_(2(q−a)−3(1−b))H_(2a−3b) where q≦30, 0≦a≦q and b=0 or 1.

A five- to six-membered heterocyclic compound comprising oxygen, nitrogen and/or sulphur atoms optionally substituted by functional groups, aryl, alkyl, aryloxy, alkyloxy, halogen, heteroatoms and/or heterocyclic compounds preferably comprises furyl, thiophenyl, pyrryl, pyridyl, indolyl, benzoxazolyl, dioxolyl, dioxyl, benzimidazolyl, benzthiazolyl, dimethylpyridyl, methylchinolyl, dimethylpyrryl, methoxyfuryl, dimethoxypyridyl or difluorpyridyl.

If two neighbouring groups together form an unsaturated, saturated or aromatic ring optionally substituted by functional groups, aryl, alkyl, aryloxy, alkyloxy, halogen, heteroatoms and/or heterocyclic compounds and optionally interrupted by one or more oxygen and/or sulphur atoms and/or one or more substituted or unsubstituted imino groups, this preferably comprises 1,3-propylene, 1,4-butylene, 1,5-pentylene, 2-oxa-1,3-propylene, 1-oxa-1,3-propylene, 2-oxa-1,3-propylene, 1-oxa-1,3-propenylene, 3-oxa-1,5-pentylene, 1-aza-1,3-propenylene, 1-C1-C4-aAlkyl-1-aza-1,3-propenylene, 1,4-buta-1,3-dienylene, 1-aza-1,4-buta-1,3-dienylene or 2-aza-1,4-buta-1,3-dienylene.

If the aforesaid groups contain oxygen and/or sulphur atoms and/or substituted or unsubstituted imino groups, the number of oxygen and/or sulphur atoms and/or imino groups is not restricted. Usually these amount to no more than 5 in the group, preferably no more than 4 and quite particularly preferably no more than 3.

If the aforesaid groups contain heteroatoms, usually at least one carbon atom, preferably at least two carbon atoms are found between two heteroatoms.

Particularly preferably the groups R¹ to R⁹ independently of one another denote

hydrogen;

unbranched or branched, unsubstituted or singly to multiply substituted with hydroxy, halogen, phenyl, cyano, C₁-C₆-alkoxycarbonyl and/or sulphonic acid, C₁-C₁₈-Alkyl having a total of 1 to 20 carbon atoms such as, for example, methyl, ethyl, 1-propyl, 2-propyl, 1-butyl, 2-butyl, 2-methyl-1-propyl (isobutyl), 2-methyl-2-propyl (tert.-butyl), 1-pentyl, 2-pentyl, 3-pentyl, 2 methyl-1-butyl, 3-methyl-1-butyl, 2-methyl-2-butyl, 3-methyl-2-butyl, 2,2-dimethyl-1-propyl, 1-hexyl, 2-hexyl, 3-hexyl, 2-methyl-1-pentyl, 3-methyl-1-pentyl, 4-methyl-1-pentyl, 2-methyl-2-pentyl, 3-methyl-2-pentyl, 4 methyl-2-pentyl, 2 methyl-3-pentyl, 3-methyl-3-pentyl, 2,2-dimethyl-1-butyl, 2,3 dimethyl-1-butyl, 3,3-dimethyl-1-butyl, 2-ethyl-1-butyl, 2,3-dimethyl-2-butyl, 3,3 dimethyl-2-butyl, 1-heptyl, 1-octyl, 1-nonyl, 1-decyl, 1-undecyl, 1-dodecyl, 1 tetradecyl, 1-hexadecyl, 1-octadecyl, 2-hydroxyethyl, benzyl, 3-phenylpropyl, 2 cyanoethyl, 2 (methoxycarbonyl)-ethyl, 2-(ethoxycarbonyl)-ethyl, 2-(n-butoxy-carbonyl)-ethyl, trifluoromethyl, difluoromethyl, fluoromethyl, pentafluoroethyl, heptafluoropropyl, heptafluoroisopropyl, nonafluorobutyl, nonafluoroisobutyl, undecylfluoropentyl, undecylfluoroisopentyl, 6-hydroxyhexyl and propylsulphonic acid; glycols, butylene glycols and oligomers thereof having 1 to 100 units and one hydrogen or one C₁-C₈-alkyl as the terminal group, such as, for example, R^(A)O—(CHR^(B)—CH₂—O)_(p)—CHR^(B)—CH₂— or R^(A)O—(CH₂CH₂CH₂CH₂O)_(p)—CH₂CH₂CH₂CH₂O— where R^(A) and R^(B) are preferably hydrogen, methyl or ethyl and p is preferably 0 to 3, in particular 3-oxabutyl, 3-oxapentyl, 3,6-dioxaheptyl, 3,6-dioxaoctyl, 3,6,9-trioxadecyl, 3,6,9-trioxa-undecyl, 3,6,9,12-tetraoxatridecyl and 3,6,9,12-tetraoxatetradecyl;

vinyl; and

N,N-Di-C₁-C₆-alkyl-amino, such as, for example, N,N-dimethylamino and N,N-diethyl-amino.

Quite particularly preferably the groups R¹ to R⁹ independently of one another stand for hydrogen or C₁-C₁₈-alkyl, such as for example methyl, ethyl, 1-butyl, 1-pentyl, 1-hexyl, 1-heptyl, 1-octyl, for phenyl, for 2-hydroxyethyl, for 2-cyanoethyl, for 2-(methoxycarbonyl)ethyl, for 2-(ethoxycarbonyl)ethyl, for 2-(N-butoxycarbonyl)ethyl, for N,N-dimethylamino, for N,N-diethylamino, for chlorine and for CH₃O—(CH₂CH₂O)_(p)—CH₂CH₂— and CH₃CH₂O—(CH₂CH₂O)_(p)CH₂CH₂— where p is 0 to 3.

Quite particularly preferred are ionic liquids in which the cation [A]⁺ is a pyridinium ion (IVa) in which

one of the groups R¹ to R⁵ methyl, ethyl or chlorine and the remaining groups R¹ to R⁵ are hydrogen;

R³ is dimethylamino and the remaining groups R¹, R², R⁴ and R⁵ are hydrogen;

all the groups R¹ to R⁵ are hydrogen;

R² is carboxy or carboxamide and the remaining groups R¹, R², R⁴ and R⁵ are hydrogen; or

R¹ and R² or R² and R³ is 1,4-buta-1,3-dienylene and the remaining groups R¹, R², R⁴ and R⁵ are hydrogen;

and in particular one such in which

R¹ to R⁵ are hydrogen; or

one of the groups R¹ to R⁵ is methyl or ethyl and the remaining groups R¹ to R⁵ are hydrogen.

As quite particularly preferred pyridinium ions (IVa) mention may be made of 1-methylpyridinium, 1-ethylpyridinium, 1-(1-butyl)pyridinium, 1-(1-hexyl)pyridinium, 1-(1-octyl)pyridinium, 1-(1-hexyl)-pyridinium, 1-(1-octyl)-pyridinium, 1-(1-dodecyl)-pyridinium, 1-(1-tetradecyl)-pyridinium, 1-(1-hexadecyl)-pyridinium, 1,2-dimethylpyridinium, 1-ethyl-2-methylpyridinium, 1-(1-butyl)-2-methylpyridinium, 1-(1-hexyl)-2-methylpyridinium, 1-(1-octyl)-2-methylpyridinium, 1-(1-dodecyl)-2-methylpyridinium, 1-(1-tetradecyl)-2-methylpyridinium, 1-(1-hexadecyl)-2-methylpyridinium, 1-methyl-2-ethylpyridinium, 1,2-diethylpyridinium, 1-(1-butyl)-2-ethylpyridinium, 1-(1-hexyl)-2-ethylpyridinium, 1-(1-octyl)-2-ethylpyridinium, 1-(1-dodecyl)-2-ethylpyridinium, 1-(1-tetradecyl)-2-ethylpyridinium, 1-(1-hexadecyl)-2-ethylpyridinium, 1,2-dimethyl-5-ethyl-pyridinium, 1,5-diethyl-2-methyl-pyridinium, 1-(1-butyl)-2-methyl-3-ethyl-pyridinium, 1-(1-hexyl)-2-methyl-3-ethyl-pyridinium and 1-(1-octyl)-2-methyl-3-ethyl-pyridinium, 1-(1-dodecyl)-2-methyl-3-ethyl-pyridinium, 1-(1-tetradecyl)-2-methyl-3-ethyl-pyridinium and 1-(1-hexadecyl)-2-methyl-3-ethyl-pyridinium.

Quite particularly preferred are ionic liquids in which the cation [A]⁺ is a pyridazinium ion (IVb) in which

R¹ to R⁴ are hydrogen; or

one of the groups R¹ to R⁴ is methyl or ethyl and the remaining groups R¹ to R⁴ are hydrogen.

Quite particularly preferred are ionic liquids in which the cation [A]⁺ is a pyrimidinium ion (IVc) in which

R¹ is hydrogen, methyl or ethyl and R² to R⁴ independently of one another are hydrogen or methyl; or

R¹ is hydrogen, methyl or ethyl, R² and R⁴ are methyl and R³ is hydrogen.

Quite particularly preferred are ionic liquids in which the cation [A]⁺ is a pyrazinium ion (IVd) in which

R¹ is hydrogen, methyl or ethyl and R² to R⁴ are independently of one another hydrogen or methyl;

R¹ is hydrogen, methyl or ethyl, R² and R⁴ are methyl and R³ is hydrogen;

R¹ to R⁴ are methyl; or

R¹ to R⁴ are methyl [or] hydrogen.

Quite particularly preferred are ionic liquids in which the cation [A]⁺ is an imidazolium ion (IVe) in which

R¹ is hydrogen, methyl, ethyl, 1-propyl, 1-butyl, 1-pentyl, 1-hexyl, 1-octyl, 2-hydroxyethyl or 2-cyanoethyl and R² to R⁴ independently of one another are hydrogen, methyl or ethyl.

As quite particularly preferred imidazolium ions (IVe) mention may be made of 1-methylimidazolium, 1-ethylimidazolium, 1-(1-butyl)-imidazolium, 1-(1-octyl)-imidazolium, 1-(1-dodecyl)-imidazolium, 1-(1-tetradecyl)-imidazolium, 1-(1-hexadecyl)-imidazolium, 1,3-dimethylimidazolium, 1-ethyl-3-methylimidazolium, 1-(1-butyl)-3-methylimidazolium, 1-(1-butyl)-3-ethylimidazolium, 1-(1-hexyl)-3-methyl-imidazolium, 1-(1-hexyl)-3-ethylimidazolium, 1-(1-hexyl)-3-butyl-imidazolium, 1-(1-octyl)-3-methylimidazolium, 1-(1-octyl)-3-ethylimidazolium, 1-(1-octyl)-3-butylimidazolium, 1-(1-dodecyl)-3-methylimidazolium, 1-(1-dodecyl)-3-ethylimidazolium, 1-(1-dodecyl)-3-butylimidazolium, 1-(1-dodecyl)-3-octylimidazolium, 1-(1-tetradecyl)-3-methylimidazolium, 1-(1-tetradecyl)-3-ethylimidazolium, 1-(1-tetradecyl)-3-butylimidazolium, 1-(1-tetradecyl)-3-octylimidazolium, 1-(1-hexadecyl)-3-methylimidazolium, 1-(1-hexadecyl)-3-ethylimidazolium, 1-(1-hexadecyl)-3-butylimidazolium, 1-(1-hexadecyl)-3-octylimidazolium, 1,2-dimethylimidazolium, 1,2,3-trimethylimidazolium, 1-ethyl-2,3-dimethylimidazolium, 1-(1-butyl)-2,3-dimethylimidazolium, 1-(1-hexyl)-2,3-dimethyl-imidazolium, 1-(1-octyl)-2,3-dimethylimidazolium, 1,4-dimethylimidazolium, 1,3,4-trimethylimidazolium, 1,4-dimethyl-3-ethylimidazolium, 3-butylimidazolium, 1,4-dimethyl-3-octylimidazolium, 1,4,5-trimethylimidazolium, 1,3,4,5-tetramethylimidazolium, 1,4,5-trimethyl-3-ethylimidazolium, 1,4,5-trimethyl-3-butylimidazolium and 1,4,5-trimethyl-3-octylimidazolium.

Quite particularly preferred are ionic liquids in which the cation [A]⁺ is a pyrazolium ion (IVf), (IVg) or (IVg′), in which

R¹ is hydrogen, methyl or ethyl and R² to R⁴ independently of one another are hydrogen or methyl.

Quite particularly preferred are ionic liquids in which the cation [A]⁺ is a pyrazolium ion (IVh) in which

R¹ to R⁴ independently of one another are hydrogen or methyl.

Quite particularly preferred are ionic liquids in which the cation [A]⁺ is a 1-pyrazolinium ion (IVi) in which

R¹ to R⁶ independently of one another are hydrogen or methyl.

Quite particularly preferred are ionic liquids in which the cation [A]⁺ is a 2-pyrazolinium ion (IVj′) in which

R¹ is hydrogen, methyl, ethyl or phenyl and R² to R⁶ independently of one another are hydrogen or methyl.

Quite particularly preferred are ionic liquids in which the cation [A]⁺ is a 3-pyrazolinium ion (IVk) or (IVk′) in which

R¹ and R² independently of one another are hydrogen, methyl, ethyl or phenyl, and R³ to R⁶ independently of one another are hydrogen or methyl.

Quite particularly preferred are ionic liquids in which the cation [A]⁺ is an imidazolinium ion (Ivl) in which

R¹ and R² independently of one another are hydrogen, methyl, ethyl, 1-butyl or phenyl, R³ and R⁴ independently of one another are hydrogen, methyl or ethyl and R⁵ and R⁶ independently of one another are hydrogen or methyl.

Quite particularly preferred are ionic liquids in which the cation [A]⁺ is an imidazolinium ion (IVm) or (IVm′), in which

R¹ and R² independently of one another are hydrogen, methyl or ethyl and R³ to R⁶ independently of one another are hydrogen or methyl.

Quite particularly preferred are ionic liquids in which the cation [A]⁺ is an imidazolinium ion (IVn) or (IVn′), in which

R¹ to R³ independently of one another are hydrogen, methyl or ethyl and R⁴ to R⁶ independently of one another are hydrogen or methyl.

Quite particularly preferred are ionic liquids in which the cation [A]⁺ is a thiazolium ion (IVo) or (IVo′) and is an oxazolium ion (IVp) in which

R¹ is hydrogen, methyl, ethyl or phenyl and R² and R³ independently of one another are hydrogen or methyl.

Quite particularly preferred are ionic liquids in which the cation [A]⁺ is a 1,2,4-triazolium ion (IVq), (IVq′) or (IVq″) in which

R¹ and R² independently of one another are hydrogen, methyl, ethyl or phenyl and R³ is hydrogen, methyl or phenyl.

Quite particularly preferred are ionic liquids in which the cation [A]⁺ is a 1,2,3-triazolium ion (IVr), (IVr′) or (IVr″) in which

R¹ is hydrogen, methyl or ethyl and R² and R³ independently of one another are hydrogen or methyl, or R² and R³ together is 1,4-buta-1,3-dienylene.

Quite particularly preferred are ionic liquids in which the cation [A]⁺ is a pyrrolidinium ion (IVs) in which

R¹ is hydrogen, methyl, ethyl or phenyl and R² to R⁹ independently of one another are hydrogen or methyl.

Quite particularly preferred are ionic liquids in which the cation [A]⁺ is an imidazolidinium ion (IVt) in which

R¹ and R⁴ independently of one another are hydrogen, methyl, ethyl or phenyl and R² and R³ as well as R⁵ to R⁸ independently of one another are hydrogen or methyl.

Quite particularly preferred are ionic liquids in which the cation [A]⁺ is an ammonium ion (IVu) in which

R¹ to R³ independently of one another are C₁-C₁₈-alkyl; or

R¹ to R³ independently of one another are hydrogen or C₁-C₁₈-alkyl and R⁴ is 2-hydroxyethyl; or

R¹ and R² together are 1,5-pentylene or 3-oxa-1,5-pentylene and R³ is C₁-C₁₈-alkyl, 2-hydroxyethyl or 2-cyanoethyl.

As quite particularly preferred ammonium ions (IVu) mention may be made of methyl-tri-(1-butyl)-ammonium, 2-hydroxyethyl-ammonium, N,N-dimethylpiperidinium and N,N-dimethylmorpholinium.

Quite particularly preferred are ionic liquids in which the cation [A]⁺ is a guanidinium ion (IVv) in which

R¹ to R⁵ are methyl.

As a quite particularly preferred guanidinium ion (IVv) mention may be made of N,N,N′,N′,N″,N″-hexamethylguanidinium.

Quite particularly preferred are ionic liquids in which the cation [A]⁺ is a cholinium ion (IVw) in which

R¹ and R² independently of one another are methyl, ethyl, 1-butyl or 1-octyl and R³ is hydrogen, methyl, ethyl, acetyl, —SO₂OH or —PO(OH)₂;

R¹ is methyl, ethyl, 1-butyl or 1-octyl, R² is a —CH₂—CH₂—OR⁴-group and R³ and R⁴ independently of one another are hydrogen, methyl, ethyl, acetyl, —SO₂OH or —PO(OH)₂; or

R¹ is a —CH₂—CH₂—OR⁴-group, R² is a —CH₂—CH₂—OR⁵-group and R³ to R⁵ independently of one another are hydrogen, methyl, ethyl, acetyl, —SO₂OH or —PO(OH)₂.

Quite particularly preferred are ionic liquids in which the cation [A]⁺ is a phosphonium ion (IVx) in which

R¹ to R³ independently of one another are C₁-C₁₈-alkyl, in particular butyl, isobutyl, 1-hexyl or 1-octyl.

Among the aforesaid cations, the pyridinium ions (IVa), imidazolium ions (IVe) and ammonium ions (IVu) are preferred, in particular 1-methylpyridinium, 1-ethylpyridinium, 1-(1-butyl)pyridinium, 1-(1-hexyl)pyridinium, 1-(1-octyl)pyridinium, 1-(1-hexyl)-pyridinium, 1-(1-octyl)-pyridinium, 1-(1-dodecyl)-pyridinium, 1-(1-tetradecyl)-pyridinium, 1-(1-hexadecyl)-pyridinium, 1,2-dimethylpyridinium, 1-ethyl-2-methylpyridinium, 1-(1-butyl)-2-methylpyridinium, 1-(1-hexyl)-2-methylpyridinium, 1-(1-octyl)-2-methylpyridinium, 1-(1-dodecyl)-2-methylpyridinium, 1-(1-tetradecyl)-2-methylpyridinium, 1-(1-hexadecyl)-2-methylpyridinium, 1-methyl-2-ethylpyridinium, 1,2-diethylpyridinium, 1-(1-butyl)-2-ethylpyridinium, 1-(1-hexyl)-2-ethylpyridinium, 1-(1-octyl)-2-ethylpyridinium, 1-(1-dodecyl)-2-ethylpyridinium, 1-(1-tetradecyl)-2-ethylpyridinium, 1-(1-hexadecyl)-2-ethylpyridinium, 1,2-dimethyl-5-ethyl-pyridinium, 1,5-diethyl-2-methyl-pyridinium, 1-(1-butyl)-2-methyl-3-ethyl-pyridinium, 1-(1-hexyl)-2-methyl-3-ethyl-pyridinium, 1-(1-octyl)-2-methyl-3-ethyl-pyridinium, 1-(1-dodecyl)-2-methyl-3-ethyl-pyridinium, 1-(1-tetradecyl)-2-methyl-3-ethyl-pyridinium, 1-(1-hexadecyl)-2-methyl-3-ethyl-pyridinium, 1-methylimidazolium, 1-ethylimidazolium, 1-(1-butyl)-imidazolium, 1-(1-octyl)-imidazolium, 1-(1-dodecyl)-imidazolium, 1-(1-tetradecyl)-imidazolium, 1-(1-hexadecyl)-imidazolium, 1,3-dimethylimidazolium, 1-ethyl-3-methylimidazolium, 1-(1-butyl)-3-methylimidazolium, 1-(1-hexyl)-3-methyl-imidazolium, 1-(1-octyl)-3-methylimidazolium, 1-(1-dodecyl)-3-methylimidazolium, 1-(1-tetradecyl)-3-methylimidazolium, 1-(1-hexadecyl)-3-methylimidazolium, 1,2-dimethylimidazolium, 1,2,3-trimethylimidazolium, 1-ethyl-2,3-dimethylimidazolium, 1-(1-butyl)-2,3-dimethylimidazolium, 1-(1-hexyl)-2,3-dimethylimidazolium and 1-(1-octyl)-2,3-dimethylimidazolium, 1,4-dimethylimidazolium, 1,3,4-trimethylimidazolium, 1,4-dimethyl-3-ethylimidazolium, 3-butylimidazolium, 1,4-dimethyl-3-octylimidazolium, 1,4,5-trimethylimidazolium, 1,3,4,5-tetramethylimidazolium, 1,4,5-trimethyl-3-ethylimidazolium, 1,4,5-trimethyl-3-butylimidazolium, 1,4,5-trimethyl-3-octylimidazolium and 2-hydroxyethy-ammonium.

The metal cations [M¹]⁺, [M²]⁺, [M³]⁺, [M⁴]²⁺ and [M⁵]³⁺ specified in formulae (IIIa) to (IIIj) generally comprise metal cations of the 1st, 2nd, 6th, 7th, 8th, 9th, 10th, 11th, 12th and 13th group of the periodic system. Suitable metal cations are, for example, Li⁺, Na⁺, K⁺, Cs⁺, Mg²⁺, Ca²⁺, Ba²⁺, Cr³⁺, Fe²⁺, Fe³⁺, Co²⁺, Ni²⁺, Cu²⁺, Ag⁺, Zn²⁺ and Al³⁺.

In principle, all anions which in combination with a cation result in an ionic liquid can be used as anions.

The anion [Y]^(n−) of the ionic liquid is, for example, selected from:

the group of halides and halogen-containing compounds having the formulae:

F⁻, Cl⁻, Br⁻, I⁻, BF₄ ⁻, PF₆ ⁻, AlCl₄ ⁻, Al₂Cl₇ ⁻, Al₃Cl₁₀ ⁻, AlBr₄ ⁻, FeCl₄ ⁻, BCl₄ ⁻, SbF₆ ⁻, AsF₆ ⁻, ZnCl₃ ⁻, SnCl₃ ⁻, CuCl₂ ⁻, CF₃SO₃ ⁻, (CF₃SO₃)₂N⁻, CF₃CO₂ ⁻, CCl₃CO₂ ⁻, CN⁻, SCN⁻, OCN⁻, NO²⁻, NO³⁻, N(CN)⁻;

the group of sulphates, sulphites and sulphonates having the general formulae:

SO₄ ²⁻, HSO₄ ⁻, SO₃ ²⁻, HSO₃ ⁻, R^(a)OSO₃ ⁻, R^(a)SO₃ ⁻;

the group of phosphates having the general formulae:

PO₄ ³⁻, HPO₄ ²⁻, H₂PO₄ ⁻, R^(a)PO₄ ²⁻, HR^(a)PO₄ ⁻, R^(a)R^(b)PO₄ ⁻;

the group of phosphonates and phosphinates having the general formulae:

R^(a)HPO₃ ⁻, R^(a)R^(b)PO₂ ⁻, R^(a)R^(b)PO₃ ⁻;

the group of phosphites having the general formulae:

PO₃ ³⁻, HPO₃ ²⁻, H₂PO₃ ⁻, R^(a)PO₃ ²⁻, R^(a)HPO₃ ⁻, R^(a)R^(b)PO₃ ⁻;

the group of phosphonites and phosphinites having the general formula:

R^(a)R^(b)PO₂ ⁻, R^(a)HPO₂ ⁻, R^(a)R^(b)PO⁻, R^(a)HPO⁻;

the group of carboxylates having the general formulae:

R^(a)COO⁻;

the group of borates having the general formulae:

BO₃ ³⁻, HBO₃ ²⁻, H₂BO₃ ⁻, R^(a)R^(b)BO₃ ⁻, R^(a)HBO₃ ⁻, R^(a)BO₃ ²⁻, B(OR^(a))(OR^(b))(OR^(c))(OR^(d))⁻, B(HSO₄)⁻, B(R^(a)SO4)⁻;

the group of boronates having the general formulae:

R^(a)BO₂ ²⁻, R^(a)R^(b)BO⁻;

the group of carbonates and carboxylic acid esters having the general formulae:

HCO₃ ⁻, CO₃ ²⁻, R^(a)CO₃ ⁻;

the group of silicate and silicic acid esters having the general formulae:

SiO₄ ⁴⁻, HSiO₄ ³⁻, H₂SiO₄ ²⁻, H₃SiO₄ ⁻, R^(a)SiO₄ ³⁻, R^(a)R^(b)SiO₄ ²⁻, R^(a)R^(b)R^(c)SiO₄ ⁻, HR^(a)SiO₄ ²⁻, H₂R^(a)SiO₄ ⁻, HR^(a)R^(b)SiO₄ ⁻;

the group of alkyl or arylsilane salts having the general formulae:

R^(a)SiO₃ ³⁻, R^(a)R^(b)SiO₂ ²⁻, R^(a)R^(b)R^(c)SiO⁻, R^(a)R^(b)R^(c)SiO₃ ⁻, R^(a)R^(b)R^(c)SiO₂ ⁻, R^(a)R^(b)SiO₃ ²⁻;

the group of carboxylic acid imides, bis(sulphonyl)imides and sulphonylimides having the general formulae:

the group of methides having the general formula:

the group of alkoxides and aryloxides having the general formulae:

R^(a)O⁻;

the group of halometallates having the general formula

[M_(r)Hal_(t)]^(s−),

wherein M denotes a metal and Hal denotes fluorine, chlorine, bromine or iodine, r and t are positive integers and define the stoichiometry of the complex and s is a positive integer and gives the charge of the complex; the group of sulphides, hydrogen sulphides, polysulphides, hydrogen polysulphides and thiolates having the general formulae:

S²⁻, HS⁻, [S_(v)]²⁻, [HS_(v)]⁻, [R^(a)S]⁻,

wherein v is a positive integer from 2 to 10;

the group of complex metal ions such as Fe(CN)₆ ³⁻, Fe(CN)₆ ⁴⁻, MnO₄ ⁻, Fe(CO)₄ ⁻.

Herein R^(a), R^(b), R^(c) and R^(d) independently of one another denote

hydrogen;

C₁-C₃₀-alkyl and the aryl-, heteroaryl-, cycloalkyl-, halogen-, hydroxy-, amino-, carboxy-, formyl-, —O—, —CO—, —CO—O— or —CO—N<substituted components thereof such as methyl, ethyl, 1-propyl, 2-propyl, 1-butyl, 2-butyl, 2-methyl-1-propyl (isobutyl), 2-methyl-2-propyl (tert.-butyl), 1-pentyl, 2-pentyl, 3-pentyl, 2-methyl-1-butyl, 3-methyl-1-butyl, 2-methyl-2-butyl, 3-methyl-2-butyl, 2,2-dimethyl-1-propyl, 1-hexyl, 2-hexyl, 3-hexyl, 2-methyl-1-pentyl, 3-methyl-1-pentyl, 4-methyl-1-pentyl, 2-methyl-2-pentyl, 3-methyl-2-pentyl, 4-methyl-2-pentyl, 2-methyl-3-pentyl, 3-methyl-3-pentyl, 2,2-dimethyl-1-butyl, 2,3-dimethyl-1-butyl, 3,3-dimethyl-1-butyl, 2-ethyl-1-butyl, 2,3-dimethyl-2-butyl, 3,3-dimethyl-2-butyl, heptyl, octyl, nonyl, decyl, undecyl, dodecyl, tridecyl, tetradecyl, pentadecyl, hexadecyl, heptadecyl, octadecyl, nonadecyl, icosyl, henicosyl, docosyl, tricosyl, tetracosyl, pentacosyl, hexacosyl, heptacosyl, octacosyl, nonacosyl, triacontyl, phenylmethyl (benzyl), diphenylmethyl, triphenylmethyl, 2-phenylethyl, 3-phenylpropyl, cyclopentylmethyl, 2-cyclopentylethyl, 3-cyclopentylpropyl, cyclohexylmethyl, 2-cyclohexylethyl, 3-cyclohexylpropyl, methoxy, ethoxy, formyl, acetyl or C_(q)F_(2(q−a)+(1−b))H_(2a+b) where q≦30, 0≦a≦q and b=0 or 1 (for example, CF₃, C₂F₅, CH₂CH₂—C_((q−2))F_(2(q−2)+1), C₆F₁₃, C₈F₁₇, C₁₀F₂₁, C₁₂F₂₅);

C₃-C₁₂-cycloalkyl and the aryl-, heteroaryl-, cycloalkyl-, halogen-, hydroxy-, amino-, carboxy-, formyl-, —O—, —CO— or —CO—O-substituted components thereof such as, for example, cyclopentyl, 2-methyl-1-cyclopentyl, 3-methyl-1-cyclopentyl, cyclohexyl, 2-methyl-1-cyclohexyl, 3-methyl-1-cyclohexyl, 4-methyl-1-cyclohexyl or C_(q)F_(2(q−a)−(1−b))H_(2a−b) where q≦30, 0≦a≦q and b=0 or 1;

C₂-C₃₀-alkenyl, and the aryl-, heteroaryl-, cycloalkyl-, halogen-, hydroxy-, amino-, carboxy-, formyl-, —O—, —CO— or —CO—O-substituted components thereof such as, for example, 2-propenyl, 3-butenyl, cis-2-butenyl, trans-2-butenyl or C_(q)F_(2(q−a)−(1−b))H_(2a−b) where q≦30, 0≦a≦q and b=0 or 1;

C₃-C₁₂-cycloalkenyl and the aryl-, heteroaryl-, cycloalkyl-, halogen-, hydroxy-, amino-, carboxy-, formyl-, —O—, —CO— or —CO—O-substituted components thereof such as 3-cyclopentenyl, 2-cyclohexenyl, 3-cyclohexenyl, 2,5-cyclohexadienyl or C_(q)F_(2(q−a)−3(1−b))H_(2a−3b) where q≦30, 0≦a≦q and b=0 or 1;

aryl or heteroaryl having 2 to 30 carbon atoms and the alkyl-, aryl-, heteroaryl-, cycloalkyl-, halogen-, hydroxy-, amino-, carboxy-, formyl-, —O—, —CO— or —CO—O-substituted components thereof such as phenyl, 2-methyl-phenyl (2-tolyl), 3-methyl-phenyl (3-tolyl), 4-methyl-phenyl, 2-ethyl-phenyl, 3-ethyl-phenyl, 4-ethyl-phenyl, 2,3-dimethyl-phenyl, 2,4-dimethyl-phenyl, 2,5-dimethyl-phenyl, 2,6-dimethyl-phenyl, 3,4-dimethyl-phenyl, 3,5-dimethyl-phenyl, 4-phenyl-phenyl, 1-naphthyl, 2-naphthyl, 1-pyrrolyl, 2-pyrrolyl, 3-pyrrolyl, 2-pyridinyl, 3-pyridinyl, 4-pyridinyl or C₆F_((5−a))H_(a) where 0≦a≦5; or

two groups are an unsaturated, saturated or aromatic ring, optionally substituted by functional groups, aryl, alkyl, aryloxy, alkyloxy, halogen, heteroatoms and/or heterocyclic compounds and optionally interrupted by one or more sulphur atoms and/or one or more substituted or unsubstituted imino groups.

Quite particularly preferred anions are chloride; bromide; iodide; thiocyanate; hexafluorophosphate; trifluormethylsulphonate; methylsulphonate; formate; acetate; mandelate; nitrate; nitrite; trifluoracetate; sulphate; hydrogen sulphate; methylsulphate; ethylsulphate; 1-propylsulphate; 1-butylsulphate; 1-hexylsulphate; 1-octylsulphate, phosphate; dihydrogen phosphate; hydrogen phosphate; C₁-C₄-dialkylphosphate, propionate; tetrachloroaluminate; Al₂Cl₇ ⁻; chlorozincate; chloroferrate; bis(trifluoromethylsulphonyl)imide; bis(pentafluoroethylsulphonyl)imide; bis(methylsulphonyl)imide; bis(p-tolylsulphonyl)imide; tris(trifluoromethylsulphonyl)methide; bis(pentafluoroethylsulphonyl)methide; p-tolylsulphonate; tetracarbonylcobaltate; dimethylenglycol monomethylethersulphate; oleate; stearate; acrylate; methacrylate; maleinate; hydrogen citrate; vinylphosphonate; bis(pentafluoroethyl)phosphinate; borates such as bis[salicylato(2-)]borate, bis[oxalato(2-)]borate, bis[1,2-benzoldiolato(2)-O,O′]borate, tetracyanoborate, tetrafluoroborate; dicyanamide; tris(pentafluoroethyl)trifluorophosphate; tris(heptafluoropropyl)trifluorophosphate, cyclic arylphosphates such as brenzcatecholphosphate (C₆H₄O₂)P(O)O⁻ and chlorocobaltate.

Quite particularly preferred anions are

Chloride, bromide, hydrogen sulphate, tetrachloroaluminate, thiocyanate, methylsulphate, ethylsulphate, methylsulphonate, formiate, acetate, dimethylphosphate, diethylphosphate, p-tolylsulphonate, tetrafluoroborate and hexafluorophosphate.

Particularly preferred are ionic liquids which contain as cation

methyl-tri-(1-butyl)-ammonium, 2-hydroxyethylammonium, 1-methylimidazolium, 1-ethylimidazolium, 1-(1-butyl)-imidazolium, 1-(1-octyl)-imidazolium, 1-(1-dodecyl)-imidazolium, 1-(1-tetradecyl)-imidazolium, 1-(1-hexadecyl)-imidazolium, 1,3-dimethylimidazolium, 1-ethyl-3-methylimidazolium, 1-(1-butyl)-3-methylimidazolium, 1-(1-butyl)-3-ethylimidazolium, 1-(1-hexyl)-3-methyl-imidazolium, 1-(1-hexyl)-3-ethyl-imidazolium, 1-(1-hexyl)-3-butyl-imidazolium, 1-(1-octyl)-3-methylimidazolium, 1-(1-octyl)-3-ethylimidazolium, 1-(1-octyl)-3-butylimidazolium, 1-(1-dodecyl)-3-methylimidazolium, 1-(1-dodecyl)-3-ethylimidazolium, 1-(1-dodecyl)-3-butylimidazolium, 1-(1-dodecyl)-3-octylimidazolium, 1-(1-tetradecyl)-3-methylimidazolium, 1-(1-tetradecyl)-3-ethylimidazolium, 1-(1-tetradecyl)-3-butylimidazolium, 1-(1-tetradecyl)-3-octylimidazolium, 1-(1-hexadecyl)-3-methylimidazolium, 1-(1-hexadecyl)-3-ethylimidazolium, 1-(1-hexadecyl)-3-butylimidazolium, 1-(1-hexadecyl)-3-octylimidazolium, 1,2-dimethylimidazolium, 1,2,3-trimethylimidazolium, 1-ethyl-2,3-dimethylimidazolium, 1-(1-butyl)-2,3-dimethylimidazolium, 1-(1-hexyl)-2,3-dimethyl-imidazolium, 1-(1-octyl)-2,3-dimethylimidazolium, 1,4-dimethylimidazolium, 1,3,4-trimethylimidazolium, 1,4-dimethyl-3-ethylimidazolium, 3-butylimidazolium, 1,4-dimethyl-3-octylimidazolium, 1,4,5-trimethylimidazolium, 1,3,4,5-tetramethylimidazolium, 1,4,5-trimethyl-3-ethylimidazolium, 1,4,5-trimethyl-3-butylimidazolium or 1,4,5-trimethyl-3-octylimidazolium;

and as anion

chloride, bromide, hydrogen sulphate, tetrachloroaluminate, thiocyanate, methylsulphate, ethylsulphate, methylsulphonate, formiate, acetate, dimethylphosphate, diethylphosphate, p-tolylsulphonate, tetrafluoroborate and hexafluorophosphate.

Furthermore particularly preferred are the following ionic liquids:

1,3-dimethylimidazolium-methylsulphate, 1,3-dimethylimidazolium-hydrogensulphate, 1,3-dimethylimidazolium-dimethylphosphate, 1-ethyl-3-methylimidazolium-methylsulphate, 1-ethyl-3-methylimidazolium-trifluormethylsulphonate, 1-ethyl-3-methylimidazolium-hydrogensulphate, 1-ethyl-3-methylimidazolium thiocyanate, 1-ethyl-3-methylimidazolium acetate, 1-ethyl-3-methylimidazolium methylsulphonate, 1-ethyl-3-methylimidazolium diethylphosphate, 1-(1-butyl)-3-methylimidazolium methylsulphate, 1-(1-butyl)-3-methylimidazolium hydrogensulphate, 1-(1-butyl)-3-methylimidazolium thiocyanate, 1-(1-butyl)-3-methylimidazolium acetate, 1-(1-butyl)-3-methylimidazolium methylsulphonate, 1-(1-dodecyl)-3-methylimidazolium methylsulphate, 1-(1-dodecyl)-3-methylimidazolium hydrogen sulphate, 1-(1-tetradecyl)-3-methylimidazolium methylsulphate, 1-(1-tetradecyl)-3-methylimidazolium hydrogen sulphate, 1-(1-hexadecyl)-3-methylimidazolium methylsulphate or 1-(1-hexadecyl)-3-methylimidazolium hydrogen sulphate, 1-hexyl-3-methylimidazolium trifluormethylsulphonate, 1-hexyl-3-methylimidazolium methylsulphonate 1-butyl-3-methylimidazolium trifluoromethylsulphonate, tetrabutylphosphonium methylsulphonate, tetrabutylphosphonium trifluoromethylsulphonate, tetramethylphosphonium methylsulphonate, tetramethylphosphonium trifluoromethylsulphonate, tributylmethylphosphonium methylsulphonate, tributylmethylphosphonium trifluoromethylsulphonate or 2-hydroxyethylammonium formiate.

The invention is described in detail hereinafter with reference to figures. The following is shown in detail therein:

FIG. 1 shows a schematic diagram of an apparatus for executing a steam cycle process which is used to implement the operating method according to the invention.

FIG. 2 shows an alternative embodiment to the apparatus from FIG. 1.

FIG. 3 shows a further configuration of a steam cycle process apparatus for using the ionic liquid used for frost protection as lubricant.

FIG. 1 shows in schematic simplified form the basic components for an apparatus for executing a steam cycle process 1. As possible embodiments the steam process 1 can be executed as a Clausius-Rankine process or as a cyclic process of the Kalina type. In the latter case the working medium consists of several components which go over into the vapour phase at different temperature levels.

A reservoir for the operating fluid 2 supplies the operating fluid as liquid phase. From there it is typically supplied to the steam generator 3 by means of a feed pump 8 which is advantageously configured as variable-speed for adaptation of the volume flow. The vapour phase generated there enters into the expander 4 and performs mechanical work by expanding. Subsequently, a condensation takes place in the condenser 5 and the condensate is returned.

According to the invention, in addition to the working medium provided for the evaporation in the steam generator 3, the operating fluid comprises an ionic liquid as a frost protection agent. Accordingly, the melting point of the mixture of working medium and ionic liquid is lower than the freezing point of the pure working medium. If water is used as the working medium, for example, 1-ethyl-3-methylimidazolium-methylsulphonate (EMIM MeSO₃) can be used as ionic liquid. In pure form EMIN MeSO₃ has a melting point of 35° C. In a mixture with water having a water fraction of 20 gw. %, the glass transition for the mixture lies at a temperature below −100° C. With increasing water content, the melting point increases and for a weight fraction of 80 gw. % water is −10° C. For the typically approximately compensated weight ratio present when the steam cycle process apparatus is at a standstill, that is a 50:50 mixture in relation to the weight fraction, the melting point of the mixture is advantageously low at −36° C. A mixture of 1-ethyl-3-methylimidazolium hydrogen sulphate as ionic liquid and water as working medium has similar values. Furthermore, tetramethylammonium-methylsulphonate can be used as ionic liquid for mixing with water if the water content is at least 34 gw. %. Thus, the melting point for this mixture at least in a mixing ratio having a weight fraction of water of 50-80 gw. % lies below −20° C. Other mixtures of ionic liquid to water in a weight ratio of 60:40 or 50:50 having a melting point of less than −20° C. can comprise as possible ionic liquids 1,2,3-trimethylimidazolium-methylsulphonate, ethyltrimethylammonium-methylsulphonate, tris-(2-hydroxyethyl)methylammonium-methylsulphonate, diethyldimethylammonium-methylsulphonate, N-dimethylmorpholinium-methylsulphonate, methylimidazolium-butansulphonate, N-methyl-pyridinium-methylsulphonate, N-ethyl-pyridinium-methylsulphonate.

During operation of the steam generator 3 the ionic liquid produces a partial pressure which substantially tends to zero. Accordingly, the cation/anion pairing of the ionic liquid is selected so that the decomposition temperature lies above the operating temperature in the steam generator 3. In this case, it is possible that the steam generator 3 is configured such that at least during a certain operating phase the temperature in the liquid phase of the operating fluid in the steam generator 3 is set below the decomposition temperature of the ionic liquid. Accordingly, in parts of the steam generator 3 in which only the working medium is present as vapour phase, it is possible to allow temperatures above the decomposition temperature or to provide an operating phase which, after removal of the ionic liquid from the operating fluid, allows a temperature, at least for parts of the steam generator 3, which lies above the decomposition temperature of the ionic liquid. As a result of previously described measure, it is ensured that the ionic liquid remains stable in the steam generator 3 and does not go over into the vapour phase apart from entrainment of droplets and thus can be removed in liquid form from the steam generator 3.

According to a first embodiment which is sketched in FIG. 1, after passing through the steam generator 3, the ionic liquid is returned to the reservoir for the operating fluid 2 by means of a bypass line 10. In addition, a tank is provided for the operating medium 6 in which the condensate from the condenser 5 collects. The condensate should contain substantially no ionic liquid. Consequently, after a certain operating temperature is reached, for example, a certain threshold temperature in the reservoir for the operating fluid 2, it is possible to remove the ionic liquid at least partly from the operating fluid so that no unused removal of heat from the steam generator results. For this purpose, it is preferable to take a weight fraction of at least 50% of the ionic liquid originally present in the operating fluid from the steam cycle process. The removal of a higher fraction, in particular of 80% and more, is preferred, particularly preferably at least 95%.

According to the diagram shown in FIG. 1, the removal of the ionic liquid from the operating fluid is accomplished by the evaporation of the working medium in the steam generator 3 and its collection in the tank for the working medium 6. Preferably, after reaching a certain level in the tank for the working medium 6 which corresponds to the volume of working medium required for operation of the steam cycle process 1, a valve unit 11 which controls the inflow from the tank for the working medium 6 or the reservoir for the operating fluid 2 to the steam generator 3 such that the reservoir for the operating fluid 2 is decoupled and the feed pump 8 draws exclusively from the tank for the working medium 6. This switching by means of the valve unit 11 can either be time- and/or level-controlled and/or temperature-controlled and/or controlled depending on the concentration of the ionic liquid in the operating fluid.

FIG. 2 shows a further possible embodiment of an apparatus for implementing a steam cycle process using the operating fluid according to the invention with a possibility for separating the ionic liquid from the operating fluid for a system at temperature. Unlike the embodiment according to FIG. 1, FIG. 2 shows a separate tank for the ionic liquid 7 which is connected to an outlet for the liquid phase at the steam generator 3. Accordingly, preferably the non-evaporated fractions of the operating fluid collect in the tank for the ionic liquid 7 so that an enrichment of the ionic liquid takes place here. Below the operating temperature and in particular at temperatures at which there is a risk of frost, the ionic liquid is returned from the tank for the ionic liquid 7 to the reservoir for the operating fluid 2. This can be accomplished, for example, by means of the line connection outlined in FIG. 2 and a return pump 9 provided therein. When the operating temperature is reached, this conveying stream can be reduced or returned to zero so that an enrichment of the ionic liquid in the tank for the ionic liquid 7 results during further operation of the steam generator 3 and at the same time the fraction of the ionic liquid in the reservoir for the operating fluid 2 is reduced since the condensate of the working medium is continuously supplied from the condenser 5. After a certain time, a main part and preferably substantially the entire fraction of the ionic liquid is removed from the steam cycle process. After this is achieved, according to one embodiment it is possible to close the connection between the steam generator 3 and the tank for the ionic liquid 7 and according to a possible embodiment at the steam generator, set a suitably high temperature for the exhaust steam.

A further embodiment of the invention for which the ionic liquid fulfills a double function is explained hereinafter with reference to FIG. 3. On the one hand, it serves as an additive to the working medium to achieve a sufficient frost safety, on the other hand, the ionic liquid, possibly with a residual fraction of working medium, serves as lubricant. Accordingly, the embodiment of the invention comprises a steam cycle process apparatus having an apparatus for withdrawing the ionic liquid or a mixture enriched with said liquid. The method according to the invention for this embodiment uses the withdrawal for lubricating revolving components of the steam cycle process apparatus, in particular the expander. Furthermore, the lubricant can be used for further moving components outside the steam cycle process apparatus. In the event that a hybrid drive comprising a steam engine and an internal combustion engine is provided, it is possible in particular to achieve the lubrication of the internal combustion engine by means of a lubricant containing the ionic liquid.

In detail, the basic components for implementing the steam cycle process 1 are shown in the schematically simplified diagram of FIG. 3. A reservoir is provided for the operating fluid 2 which at least in the rest state holds a mixture of the working medium and the ionic liquid for frost protection purposes. This mixture is conveyed by means of the feed pump 8 which supplies this to the steam generator 3. The steam generator 3 is exposed to a stream of hot exhaust gases via an exhaust gas duct 21 from the internal combustion engine 20 and thus enables the evaporation of the working medium. On leaving the steam generator 3, a mixture of liquid and gas phase is fed to a separator 12 which separates the vaporous working medium and supplies it to the expander 4. An additional starting valve 15 which makes it possible to bypass the expander is provided for starting up.

As a result of the partial pressure tending to zero, the ionic liquid remains liquid in the separator and can be fed from its sump to a valve device 11. The valve device 11 either allows the operating fluid to be passed via the condenser 5 and the filter 13 back to the reservoir for the operating fluid 2 or allows it to be supplied to a tank for ionic liquids 7. When the steam cycle process apparatus is at a standstill, an inflow takes place from the tank for the ionic liquid 7 to the reservoir for the operating fluid 2 by means of gravity or by a pump in order to ensure the frost-safe mixing ratio of working medium to ionic liquid there.

During operation of the steam cycle process apparatus, that is at a sufficient temperature of the steam generator 3, a mixture rich in ionic liquid is supplied to the valve device 11. With a suitable choice of the ionic liquid which exhibits both the required frost protection properties and also sufficient lubrication properties, this can be used as lubricant and as lubricant additive. The first case is shown in FIG. 3.

For lubrication the lubricant pump 16 conveys from the tank for ionic liquid 7 and supplies the lubricant to the expander 4. The lubricant is returned via the lubricant return 17. Furthermore, from the volume of air enclosed in the tank for the ionic liquid 7, a remaining residue of working medium to be evaporated can be supplied via the steam outlet 19 to the reservoir for operating fluid 2. Moreover, as a result of the operation of the expander, an unavoidable continuous leakage of working medium occurs, which flows via the return for outflowing medium 18 to the tank for the ionic liquid 7 so that an equilibrium state with a still-tolerable fraction of working medium in the lubricant circuit is established. In this context, the lubricant properties can even be satisfied with a weight fraction of 10 gw. % (percent by weight) of working medium. This will be set out hereinafter by reference to a mixture of EMIM-MeSO₃ as ionic liquid with water as working medium having a weight fraction of 5 gw. % (percent by weight).

The kinematic viscosity at a temperature of 90° C. is 5.3 cst. The density, the foam behaviour and the air separation capacity (according to DIN ISO 9120 at 50° C.) are values suitable for lubricants. The lubricant properties were measured by means of a Shell four-ball apparatus. A measurement in accordance with DIN 51350-T2 at a rotational speed of 1420 min⁻¹ gave a welding force of 2400 N. A measurement in accordance with DIN 51350-T3 at the same rotational speed and a load of 300 N yielded a ball indentation diameter of 1.04 mm. The oxidation stability and the corrosion protection behaviour were also determined, the results allowing the use as lubricant.

The aforesaid requirements on the ionic liquid relating to a low melting point in the mixture with working agents, sufficient for a frost protection agent, and a sufficiently high decomposition temperature to avoid any decomposition of the ionic liquid in the steam generator 3 are satisfied by a suitable choice for the cations and the anions of the ionic liquid. A good lubricity is additionally provided for a suitable ionic liquid. Furthermore, the cation/anion pairing is selected so that an environmentally friendly, non-toxic and reliable ionic liquid is present. In particular 1-ethyl-3-methyl-imidazolium (EMIM) is used as a possible choice for the cation and linked to an anion from the group HSO₄ ⁻, MeSO₃ and CF₃SO₃ ⁻.

Further embodiments of the invention are feasible within the scope of technical knowledge. Thus, in order to execute a Kalina process, it is possible to use a combination of different working media and provide heat sources at different temperature levels to form different vapour phases. Accordingly, it is feasible to configure the expander as multi-stage. Furthermore, it is advantageous to configure the expander such that in the event of an incipient defect in which a liquid component, for example, a fraction of the ionic liquid, enters into the expander, a sufficient water hammer resistance exists.

REFERENCE LIST

1 Steam cycle process

2 Reservoir for operating fluid

3 Steam generator

4 Expander

5 Condenser

6 Tank for working medium

7 Tank for ionic liquid

8 Feed pump

9 Return pump

10 Bypass line

11 Valve device

12 Separator

13 Filter

14 Steam line

15 Starting valve

16 Lubricant pump

17 Lubricant return

18 Return for escaping working medium

19 Steam outlet

20 Internal combustion engine

21 Exhaust gas duct 

1-23. (canceled)
 24. Operating fluid for a steam cycle process apparatus comprising: an evaporable working medium that is assigned a freezing point; and an ionic liquid having at least one organic compound as a cation, wherein the ionic liquid in pure form at a given reference pressure has a melting point which is lower than 100° C. and lies at a higher temperature than the freezing point of the working medium; and wherein the ionic liquid forms a mixture with the working medium without complex bonds and the melting point of the mixture lies below −5° C.; and the ionic liquid has a decomposition temperature which lies above the evaporation temperature of the working medium.
 25. The operating fluid according to claim 24, characterised in that the working medium comprises water.
 26. The operating fluid according to claim 24, characterised in that the decomposition temperature of the ionic liquid is higher than 200° C. and preferably higher than 300° C., and in particular higher than 350° C.
 27. The operating fluid according to claim 26, characterised in that the melting point of the ionic liquid in pure form lies in the range of 0-100° C.
 28. The operating fluid according to claim 24, characterised in that the melting point of the mixture of working medium and ionic liquid lies below −10° C. and in particular preferably below −30° C.
 29. The operating fluid according to claim 24, characterised in that the working medium and the ionic liquid have a weight fraction of at least 0.01 gw. % (percent by weight) in the mixture.
 30. The operating fluid according to claim 24, characterised in that the weight ratio of ionic liquid to working medium in the mixture is 90:10-10:90, preferably 80:20-20:80, and particularly preferably 60:40-40:60.
 31. The operating fluid according to claim 24, characterised in that the anion of the ionic liquid is a C1 to C4 alkyl sulphonate, preferably methyl sulphonate or a completely or partially fluorinated C1 to C4 alkyl sulphonate, preferably trifluoromethyl sulphonate.
 32. The operating fluid according claim 24, characterised in that the cation of the ionic liquid is pyridinium or imidazolium or phosphonium or morpholinium and the anion of the ionic liquid is a C1 to C4 alkyl sulphonate, preferably methyl sulphonate or a completely or partially fluorinated C1 to C4 alkyl sulphonate, preferably trifluoromethyl sulphonate.
 33. The operating fluid according to claim 24, characterised in that the ionic liquid comprises as cations 1-ethyl-3-methyl imidazolium (EMIM) and the anion is selected from the group formed by HSO₄ ⁻, MeSO₃ ⁻ and CF₃SO₃ ⁻.
 34. The operating fluid according to claim 24, characterised in that the operating fluid additionally is a lubricant or an addition to a lubricant.
 35. A method for operating a steam cycle process which is executed in an apparatus comprising a steam generator, an expander, a condenser and a reservoir for an operating fluid, wherein the method comprises the following process steps: when cold starting the steam cycle process, an operating fluid is supplied to the steam generator, which comprises a mixture of a working medium and an ionic liquid, wherein the ionic liquid serves as a frost protection agent and in the mixture with the working medium has a melting point which lies below −5° C., and wherein the decomposition temperature of the ionic liquid lies above the evaporation temperature of the working medium in the steam generator; in the steam generator the working medium is evaporated from the mixture and supplied in vapour form to the expander for expansion whilst performing mechanical work and then condensed in the condenser; above a predetermined operating temperature the mixture of ionic liquid and working medium is separated so that the weight fraction of the ionic liquid to the operating fluid supplied to the steam generator is reduced by at least 50% and preferably 80%, and particularly preferably 95%.
 36. The method according to claim 35, characterised in that above a predetermined operating temperature the condensate of the working medium produced in the condenser is guided into a tank for the working medium which is separate from the reservoir for the operating fluid.
 37. The method according to claim 36, characterised in that above a certain level in the separate tank for the working medium, the inflow of the operating fluid from the reservoir to the steam generator is interrupted and exclusively working medium is supplied from the separate tank for the working medium to the steam generator.
 38. The method according to claim 36, characterised in that the operating fluid not evaporated in the steam generator is supplied to a tank for the ionic liquid, which is formed separately from the reservoir for the operating fluid.
 39. The method according to claim 38, characterised in that a lubricant circuit is supplied from the tank for the ionic liquid.
 40. The method according to claim 39, characterised in that the lubricant circuit is used for lubrication of the expander.
 41. The method according to claim 39, characterised in that the steam cycle process in a vehicle is operated with an internal combustion engine and the lubricant circuit is used for the lubrication of at least one moving component of the internal combustion engine.
 42. The method according to claim 35, characterised in that the operating temperature is determined by a measurement of the temperature of the operating fluid in the reservoir.
 43. The method according to claim 35, characterised in that when the steam cycle process is at a standstill, after a predetermined time and/or below a predetermined ambient temperature the ionic liquid and the working medium are combined. 